This invention relates to a coil component and the fabrication method thereof. In particular, this invention relates to the coil component which is used as a reactor in a high-power system such as an energy control of a battery mounted on an electrically-powered car or a hybrid car including an electromotor and an internal-combustion engine.
In an electrically-powered car or a hybrid car, the coil component is driven at frequencies within the audibility range of the human ear. Specifically, the normal driving frequency of the coil component in the electrically-powered car or the hybrid car belongs to a frequency range of from several kilohertz to several tens kilohertz.
The driving frequency of the audibility range has a possibility of undesired vibration which is caused by mutual forces of attraction between coil wires or between a coil and a magnetic core. The undesired vibration makes an audible noise or whine. In addition, if the coil component has an air-gap, the coil component further has a possibility of undesired vibration caused by mutual forces of attraction between portions of the core which is provided with the air-gap. Note here that, according to the conventional techniques, there is no magnetic core structure which does not become saturated even upon a DC bias of 200 A or more without air-gaps. In other words, at least one air-gap is an absolute necessity for a superior DC bias characteristic over 200 A or more.
A known coil component is disclosed in JP-A 2001-185421. The disclosed coil component is used for a low-power and high-frequency system. The disclosed coil component comprises a coil and first and second magnetic core members. The first magnetic core member includes magnetic metal powder of 50-70%, by volume, and thermosettable resin of 50-30%, by volume. The second magnetic core member is a dust core made of sintered ferrite body or magnetic metal powder. The first and the second magnetic core members are magnetically connected in series. The coil is embedded in the first magnetic core member.
One of the purposes of JP-A 2001-185421 is to provide a magnetic component such as an inductor, a choke coil and a transformer, which can suppress noise occurrence when the magnetic component is driven.
However, note here that the actual target frequency of JP-A 2001-185421 seems to belong to a range of from several hundreds of kilohertz to several megahertz as disclosed in paragraph [0006] of JP-A 2001-185421. The target frequency of JP-A 2001-185421 far exceeds the audible frequencies. It should be also known that the high-frequency vibration of the coil component at its air-gap does not make an audible noise or whine. Therefore, it is reasonable to assume that JP-A 2001-185421 directs its attention to another noise occurrence mechanism which is quite different from the present invention.
In addition, the target of JP-A 2001-185421 is a downsized coil component for low-power system. As a matter of course, the structure of the coil component disclosed in JP-A 2001-185421 is weak in the properties of withstand voltage and resistance to undesired pulses such as surge currents.
Thus, it is conceivable that the coil component of JP-A 2001-185421 is not suitable for the high-power and low-frequency system.